There exists an acute need for screening of cargo and vehicles for detection of threat materials and illegal trade. Typically, such screening is conducted by using X-ray imaging systems in transmission mode, wherein the vehicle to be inspected is driven into an imaging facility, the driver exits the vehicle, and the X-ray scan is conducted at relatively high doses.
Scanning systems are also known in which the driver remains in the vehicle during the scan. Here, the driver drives through the X-ray system and the high energy X-ray beam is only turned on after the driver and the cab of the vehicle have passed through the inspection zone so that only the cargo is inspected. X-ray installations of this type are commonly known as portal systems.
However, the aforementioned prior art inspection systems are disadvantageous in that the cab of the vehicle is not inspected at all, thus causing a serious security gap and a potential breach in security.
Dual source approaches have also been known wherein a low-dose, low-energy X-ray source is used to scan the cab and driver when they are in the inspection zone while a high energy source is switched on when the cab has passed and the cargo is in the inspection zone. This approach works well in situations where the high energy X-ray source is in the range 2 MV and above. In lower energy systems (in the range 1 MV to 3 MV), this dual source approach can be too expensive to allow practical implementation.
Therefore, there is a need for an X-ray transmission vehicle inspection system that enables scanning of the cab portion (occupied by people, such as a driver) at low dose rate safe for human beings while allowing scanning of the cargo portion (unoccupied by people) at high dose rate. There is also a need for an X-ray cargo inspection system that can rapidly switch from low dose rate to high dose rate operating mode while striking a balance between high materials penetration for cargo portion and low intensity exposure which is safe for occupants in the cab portion of the inspected vehicle. Preferably, the vehicle inspection system allows scanning cars, buses, or other passenger vehicles in only a low dose rate mode and can be operated in dual mode when required to scan cargo vehicles that have cab and cargo container portions.